The present invention relates to elongate members for supporting and locating a load movable in opposite senses along the length of the members and in particular, to such elongate load supporting and locating members when they form part of a support structure for a coordinate machine tool.
In this specification the expression "coordinate machine tool" is intended to embrace machine tools having a working point or surface which can be located relative to a workpiece by means of "X--X" and "Y--Y" coordinates. For the avoidance of doubt, the expression coordinate machine tool includes flame cutting machines which consist essentially of a cutting torch mounted on a carriage for movement therewith. The carriage can be driven in opposite senses along a beam which in turn is mounted for movement on a pair of spaced parallel rails. The cutting torch is capable of movement in an "X--X" sense by means of the drive to the carriage and in a "Y--Y" sense by movement of the beam along the rails.
The support structure, that is, the beam and rails of a flame cutting machine must be sufficiently rigid to support the load of the cutting torch, the carriage and ancillary equipment associated therewith. The support structure must also incorporate locating surfaces in order that the cutting torch can be located accurately in the "X--X" and "Y--Y" planes with respect to a workpiece. In flame cutting machines having a tracing width of one 11/2 to 21/2 meters, and a cutting width of from 0 to 21/2 meters, the rails and the beam have to be of substantial rigidity and their very size and weight makes it difficult and expensive for locating surfaces to be machined on these parts or attached to the parts.
For example, a pair of spaced rails on a known flame cutting machine are of the locomotive type. That is to say, they resemble the rails supporting rolling stock on a railway. The rails have first to be shot-blasted for descaling purposes and then by means of a press straightened to some rough degree of alignment. They are then stress relieved to reduce rolling and bending stresses and then introduced to a machine tool for planing the top and sides of each rail. It is the planing operation which produces the accurate surfaces for location purposes. Both rails are then drilled to accommodate holding down bolts and the rails are then painted. In a typical operation this procedure can consume 81/2 hours of time.
On the same machine the beam, which is a hot-rolled box-section, is first shot-blasted and then four individual strips are first degreased, then fabricated and welded to the four corners of the box-section. Although only two of the strips are used for locating purposes, four strips have to be welded to avoid distortion during the welding operation. The welds are ground flush and then the strips are planed to provide accurate locating surfaces. The beam is then drilled and finally painted with the working surfaces of the strips being masked to avoid spoiling the locating surfaces. This operation can take up to 54 hours.